1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that develops a latent image on an image supporting member by applying a developing bias, which is a superimposed voltage of a DC voltage and an AC voltage, to a developing device.
2. Description of Related Art
As an image forming apparatus that develops a latent image on an image supporting member by applying a developing bias, which is a superimposed voltage of a DC voltage and an AC voltage, to a developing device, for example, an image forming apparatus disclosed in Japanese Patent Laid-Open Publication No. S61-166558 is known. Such an image forming apparatus (which will be hereinafter referred to as a conventional image forming apparatus) comprises image supporting members provided for a plurality of colors respectively, and developing devices provided for the plurality of colors respectively, and developing biases are applied to the respective developing devices for development of latent images formed on the image supporting members. The conventional image forming apparatus further comprises DC power circuits provided for the plurality of colors respectively to output DC components of the developing biases, and an AC power circuit for use in common to output AC components of the developing biases for all of the colors.
In the conventional image forming apparatus, however, the fact that the AC power circuit is used in common to output the AC components of the developing biases for all of the colors causes the following problem. Even in a monochromatic printing operation, toner movements from the developing devices for use in color printing to the corresponding image supporting members occur, which affects the picture quality of the developed image.